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Undeliverable Email

Posted on 2006-11-10
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Last Modified: 2010-03-06
Our email is setup through Exchange on Small Business Server.  We are having problems with sending email to some domains because our email domain we are using doesn't match the ip address we are sending the emails from.  We are not hosting our email or domain.  

Here is an example of our setup:

isp ip 100.100.100.100 (emails are sent from here)

myemaildomain.com ip 200.200.200.200

Here is the error we receive:
 <myemaildomain.com #5.5.0 smtp;521-EHLO/HELO from sender ***.***.***.100 does not map to myemaildomain.com in DNS>

What config changes should I make in order to correct this problem?
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Question by:md501
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by:Sembee
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Your reverse DNS probably doesn't match.

See my DNS Configuration guide here:

http://www.amset.info/exchange/dnsconfig.asp

Simon.
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by:nitadmin
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Are you sending all your e-mails throught ISP smtp server?
In other words are you using the ISP as a smart Host?

I strongly recommend that you don't do this. Because essentailly you are relaying all you e-mails through your ISP. Thats why you are getting this problem. You ISP is not going to change the PTR reccord for SMTP server's static ip address.

Cheers,
NITADMIN
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by:md501
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Emails are sent from exchange from ip address 100.100.100.100 which is our ISP address.  Emails are sent through myemaildomain.com which has an ip address of 200.200.200.200.  Emails aren't hosted inhouse.  Myemaildomain.com is a different company from the ISP.  

Here is an example of what shows up in email headers "from myemaildomain.com (unknown [100.100.100.100])"

Is there anyway to get our ip address off of the email headers?  Or, get our email provider's address to appear on the email headers?

Sembee - I read your article but I just don't fully understand it.
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by:Sembee
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What do you mean emails aren't hosted in house?
How does your email come in to the server? Is it delivered directly or via an SMTP feed or POP3 connector?

What didn't you understand about my article? It is basic DNS setup, which if you don't setup correctly, or get your ISP and domain name registrar to setup then your email messages will get blocked.

If you don't play by the rules, your messages will be blocked.

Simon.
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by:md501
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Simon,

Emails are downloaded by the server from the company who hosts the email through pop3 connector and then sent by smtp.

Our ISP ip address is not registered with a fqdn because another company hosts our email.

Forgive me for my ignorance.  I'm not trying to do something unethical.  I'm just trying to solve the issue of about 5-10% of our emails being undelivered through exchange.

On our workstations in outlook I have a 2nd email account setup (pop3 & smtp) which bypasses the exchange server and connects directly to the email host.  The trouble emails will go through if sent this way.  When I look at the email headers of emails sent this way in the first "from" section, it lists the email domain name and ip address not our isp ip address.

Having said all that, I would like to stop using the 2nd email account workstations and setup exchange correctly so we don't have trouble with sending emails.

I will take a look at your original article again.      
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Sembee earned 500 total points
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Who looks after your domain has no bearing on what is or is not registered with your ISP. You still need to ask your ISP to set a reverse DNS correctly. If there is no reverse DNS set on your external IP address then email messages will fail.

The server needs to be correctly resolvable on the internet.
Therefore whoever looks after your domain needs to create a new host or type A, pointing to your static IP address. I usually suggest mail, therefore creating mail.domain.com.
If you already have a host setup for OWA access for example, then you don't need to have another one configured.

Then ask your ISP to setup a reverse DNS record for that host. The ISP may tell you that it cannot because it doesn't look after your domain name. If they do say that, ask to speak to someone who understands how the internet works.

If the ISP still refuses to set a reverse DNS for your static IP address then you will have to use an SMTP Connector to route your email either through the ISPs SMTP server or through the other host. You will be unable to get your email delivered reliably without a reverse DNS record.

Simon.
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by:Stacy Spear
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Sounds like your ISP needs to be fired. They either don't care enough about you as a client (happens if they have a lot) or too ignorant to understand what needs to be done.
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by:md501
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I'm awaiting to see some results from the changes that were made with my isp.  Yes, it has taken this long for someone to listen to my requests (at the isp).  I just need a little more time to confirm some things.  
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by:redseatechnologies
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That may be so, but does not change the fact that the above is a solution to the problem.

How much longer would you like to wait before closing this?

Don't get me wrong, I am not trying to be rude, but the experts have spent their time helping you, and are effectively being penalised because your ISP is useless :)

-red
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by:md501
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Red

I understand your concern but I just need at least another day or two just so I can confirm that emails are deliverable to a specific domain.  We had a problem, made a change based on Sembee's advice, now I just need to be able to verify his advice worked.  It just took several weeks before I could get the isp to make the change.

No worries...I'll close it out soon.
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by:redseatechnologies
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md501,

Thank you for closing this old question out, it is appreciated

-red
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